High Quality Calcium Hydroxide Slurries

Abstract

A calcium hydroxide slurry is formed by combining a polymer additive with lime and water to form an aqueous slurry. The slurry so produced is viscostable, resists hard packing even after prolonged storage, is easily redispersed and has antiscaling properties. The amount of lime used is between 35 to 55% by weight of the slurry. The polymer additive is a polycarboxylate dispersing agent and is added in an amount between about 0.1 to 3% by weight of lime.

Description

CROSS REFERENCE TO RELATED APPLICATIONS[0001]The present application claims priority from a provisional application, Ser. No. 62 / 383,811, filed Sep. 6, 2016, entitled “High Quality Calcium Hydroxide Slurries”, by the same inventors.BACKGROUND OF THE INVENTION1. Field of the Invention[0002]The present invention relates generally to the preparation of stable high quality calcium hydroxide slurries with anti-scaling properties which are useful in applications such as pH control, acid neutralization and reducing calcium hardness.3. Description of the Prior Art[0003]Alkaline products which are used in adjusting pH in commercial activities, such as the treatment of sewage or wastewater, have typically employed sodium hydroxide solutions (commonly referred to as caustic) or suspensions of magnesium hydroxide. Sodium hydroxide is widely available commercially as typically found in a solution having an activity of approximately 50%. As a true solution, 50% caustic is indefinitely stable and ...

AI Technical Summary

Benefits of technology

The present invention provides a calcium hydroxide slurry that is stable, resistant to hard packing, easily redispersed, and has antiscaling properties. The slurry has a high solid content while maintaining a low viscosity. The addition of a polymer additive promotes an anti-scaling effect against calcium carbonate and calcium sulfate scale without affecting other slurry characteristics such as available lime, slurry consumption / utilization, and reactivity.

Problems solved by technology

Magnesium hydroxide, however, is not indefinitely stable without agitation, and the particles eventually settle out of suspension forming a sediment layer.

A 50% strength caustic solution can be dangerous to handle and can result in serious chemical burns if appropriate safety precautions are not followed.

Several disadvantages, however, prevent conventional lime slurries from being used where caustic soda solutions would otherwise be used.

It is difficult to produce a conventional lime slurry with a solids content of greater than about 32% without producing such a high viscosity that the material becomes unmanageable.

Typically, a viscosity above approximately 2000 cps can cause handling difficulties.

However, the effect of the gypsum is to agglomerate the lime making an abundance of large calcium hydroxide particles.

These large lime particles quickly settle from suspension and form a hard sediment that is hard to remove and causes plugging of pipes.

In addition, large lime particles react more slowly and display other detrimental characteristics.

High amounts of dispersants are undesirable in many applications.

Excess dispersant can cause foam to accumulate on the aerated waste resulting in significant processing difficulties.

Also, polymeric dispersants add to the total organic content of material treated which can be undesirable.

Further, high dispersant amounts would add considerably to the cost of producing lime slurries for use as a caustic replacement.

Another problem with creating lime slurries, especially a high solids slurry, is that such slurries can cause scaling with the equipment being used.

For example, the increase in solids can result in very high viscosities and can also lead to increased scaling in the slurry-producing, storage, conveying and dosing equipment as well as in other areas within the process afterwards.

The scaling can lead to maintenance issues, feed rate decrease, density changes and, in addition, scaling may also increase lime usage.

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